The present invention relates to couplings for connecting electric bus and, more particularly, to a coupling for connection to a bus by swaging.
Electric bus has been used for many years as an electrical conductor in a wide variety of applications. Conventional bus typically is formed in the shape of rods or tubes and is constructed from aluminum, copper or other suitable materials. The bus usually comes in sections and, therefore, must be joined together by a coupling or connector that is itself electrically conductive. In this way, the bus sections can be connected together in a variety of configurations to extend electrical circuits in electrical systems.
One of the most common types of electric bus couplings comprises a cylindrical coupling having essentially a smooth bore for receiving the bus. Once the bus is inserted into the coupling, the end of the coupling is welded to the outer surface of the inserted bus using known welding techniques. While couplings welded to bus have been generally accepted for their intended purpose, they are not without significant drawbacks.
For example, welded couplings are joined to the bus only in the area of the welded joint. This is a relatively small, annular area by comparison to the entire area of overlapping connection between the coupling and the inserted bus. As a result, any failure of the weld or the adjacent area can result in a total failure of the entire connection. In addition, heat created during the welding process anneals both the coupling and the bus in the area of the weld and the immediately surrounding areas. This causes stress concentration and, therefore, a weak link in the connection that contributes to the possibility of failure of the joint. Still further, it is difficult to inspect the integrity of a welded connection, and it is generally a dirty and relatively time-consuming process. Thus, when it is necessary to make a repair in the field, the welding time expended to make the repair can be significant. Moreover, the requirement of transporting the welding equipment to and from the repair site poses additional drawbacks.
Another matter relates to the requirement that the bus coupling be able to provide a branch connector so that electricity can be transferred via the coupling to other electrical circuits in the electrical system. At the present time, conventional couplings usually employ so-called NEMA pads to accomplish this function. A NEMA pad generally comprises a substantially flat, rectangular plate extending at a 90.degree. angle, or other suitable angle, to the outer surface of the coupling. NEMA pads are frequently required to be welded to the coupling and, therefore, they are subject to the same drawbacks discussed above with respect to the welding of couplings to the bus.
Beyond this, connections by the use of NEMA pads require that one NEMA pad be connected to another NEMA pad by conventional nuts and bolts inserted in aligned bores in the pads. When the NEMA pads are subjected to variations in temperature, they expand and contract causing separation between the pads. Vibration and other forces also can cause separation. Even minor separation undetectable to the human eye can result in hot spots, loss of current, and other undesirable effects. When this occurs, a technician must go out in the field and manually remove the bolts, clean the contacting surfaces of the NEMA pads with a wire brush, and then retighten the bolts to reconnect the pads. Experience has proven this procedure to be a relatively time-consuming, inconvenient and expensive process.
A further problem with existing couplings is that they are generally ineffective in minimizing the so-called "corona effect." The corona effect usually occurs very rapidly and, therefore, causes relatively rapid corrosion of the joint between the coupling and the bus. The corona effect also is undesirable because it drains electrical energy.
While attempts have been made to design bus couplings that avoid the foregoing problems, these couplings tend to be relatively complicated, expensive to install, or require the use of special equipment.
Accordingly, there has existed a definite need for a coupling for connecting bus which can be rapidly installed for securely connecting bus segments together, which provides a stronger and more secure connection than welded couplings, and which can be conveniently and inexpensively installed in the field, both during initial installation and when repairs are needed. The present invention satisfies these and other needs, and provides further related advantages.